Molecular devices with a spin

Abstract:

The interaction of conduction electrons with local spins in magnetic materials is at the origin of a range of intriguing phenomena. In particular the electrical conductivity becomes dependent on the magnetic configuration of the device and conversely the magnetic state of a device can be changed by a time dependent spin polarized electron current. Even more intriguing is the possibility of generating non-trivial time-dependent dynamics associated to the interaction of current electrons with the internal magnetic degrees of freedom. In this talk I will discuss two of those aspects.

First I will show how a delicate balance between molecular levels re-hybridization in an electric ﬁeld and localization can generate negative diﬀerential conductance in magnetic molecules. This is shown to depend on the magnetic state of the molecule itself, opening the opportunity for the electrical readout of the molecular state[3].

Then I will consider an intriguing eﬀect arising when the magnetic order parameter changes in time[4]. In particular I will demonstrate that the precession of a domain wall formed in a one-dimensional magnetic wire produces a net electromotive force (spin-motive force) detectable as an electrostatic DC potential. I will show that one does not need to interpret the results in terms of Barry phase, and that the whole phenomenon can be described in terms of classical mechanics. The results are obtained from classical-quantum time dependent simulations treating conduction electrons at the quantum mechanical level and the local atomic magnetizations as classical variables. In contrast to standard Ehrenfest dynamics for nuclei, where energy cannot be exchange reversibily between electrons and nuclei, this approach is entirely appropriate for spins.